This is the required version for XInput2 touch events. It also allows
to greatly simplify the code by listening to master device events only
and get rid of device id tracking:

Under XInput2 protocol version < 2.1, RawEvents are not supposed to be
sent if a pointer grab is active. However slave device events are still
received regardless of this specification and Wine implemented a
workaround to receive RawEvents during pointer grabs by listening to
these slave device events.

By advertising the support of XInput2 version >= 2.1, where RawEvents
are sent even during pointer grabs, we ensure to receive the RawMotion
even if a mouse grab is active.